This invention relates to fuel cells and, in particular, to fuel cell assemblies and components having loaded and retained catalyst therein and to apparatus and methods for performing such loading and retaining.
A fuel cell is a device which directly converts chemical energy stored in hydrocarbon fuel into electrical energy by means of an electrochemical reaction. Generally, a fuel cell comprises an anode and a cathode separated by an electrolyte, which serves to conduct electrically charged ions. In order to produce a useful power level, a number of individual fuel cells are stacked in series with an electrically conductive separator plate between each cell.
In internally reforming fuel cells, a reforming catalyst is placed within the fuel cell stack to allow direct use of hydrocarbon fuels such as methane, coal gas, etc. without the need for expensive and complex reforming equipment. In a reforming reaction, fuel cell produced water and heat are used by the reforming reaction, and the hydrocarbon fuel is internally reformed to produce hydrogen for fuel cell use. Thus, the necessary hydrogen fuel is produced by the reforming reaction, and since the reaction is endothermic, it can also be used advantageously to help cool the fuel cell stack.
Two different types of internal reforming have been developed for fuel cell assemblies. One type of internal reforming is indirect internal reforming, which is accomplished by placing the reforming catalyst in an isolated chamber within the stack and routing the reformed gas from this chamber into the anode compartment of the fuel cell. A second type of internal reforming is direct internal reforming. This type of internal reforming is accomplished by placing the reforming catalyst within the active anode compartment or fuel flow field, which provides the hydrogen produced by the reforming reaction directly to the anode.
A typical fuel cell anode compartment comprises a separator or bipolar plate for isolating fuel from the oxidant stream of the neighboring fuel cell, an anode electrode for providing electrochemical reaction sites, and an anode current collector often provided as a corrugated plate, for conducting electronic current from the anode electrode. The anode current collector is in contact with the anode electrode and also defines flow channels for the fuel gas. The reforming catalyst is placed in these flow channels to provide the direct internal reforming.
The reforming catalyst is usually available as compacted or solid particles having various solid shapes or forms such as tablet, pellet, rod, ring or sphere. However, due to the dimensions of the catalyst particles, difficulties have been encountered in trying to load the particles in the current collector channels. One difficulty is that the relatively small size of the catalyst particles makes them difficult to handle during assembly. This, in turn, makes the process of catalyst loading inefficient, and thus, unduly costly.
A second difficulty sometimes arises in achieving and maintaining a desired loading pattern of the catalyst because of the tendency of the catalyst particles to shift during the loading process and the fuel cell assembly process. The importance of the desired loading pattern stems in part from the desire to maintain a required heating profile in the fuel cell stack. This profile helps promote efficient and long term operation of the stack.
A manner of improving the efficiency and reliability of loading the catalyst particles in fuel cell components is thus always desirable. Additionally, the ability to better retain the loaded catalyst while concurrently enabling maximum operational efficiency is also a goal in the manufacturing process.